1. Field of the Invention
This invention relates generally to connectors and, more specifically, to a high performance soldering sleeve having improved heat transfer characteristics and method therefor.
2. Description of the Prior Art
During the mid 1960's, RAYCHEM CORPORATION invented the first soldering sleeve. The soldering sleeve was comprised of a heat shrinkable tube with a solder preform inside. The soldering sleeve found immediate and widespread acceptance throughout the aerospace industry. However, the soldering sleeve had one major problem. It was difficult for people who used the soldering sleeve to control the heating process to assure that excessive heat was not applied to the soldering sleeve. Excessive heat compromises the dielectric properties of the wire insulation and/or causes burned solder joints.
In the mid 1970's RAYCHEM CORPORATION made improvements to the original soldering sleeve invented in the mid 1960's. The solder preform of the original soldering sleeve was replaced with a combination of two solders which formed a bi-alloy solder ring. Each of the two solders had a different melting point. The bi-alloy solder ring was suppose to give the assembly technician using the soldering sleeve a visual cue in applying the proper amount of heat.
The 1970's improvements to the soldering sleeve provided only a marginal amount of help to the assembly technician in applying the proper amount of heat. Thus, during the 1980's RAYCHEM CORPORATION invented a thermochromic ink addition to the outside of the solder preform. The thermochromic ink ring led to a plurality of patents: U.S. Pat. No. 4,505,421; U.S. Pat. No. 4,563,224; U.S. Pat. No. 4,667,869; U.S. Pat. No. 4,688,713; and U.S. Pat. No. 4,809,901. The thermochromic ink ring was designed to undergo a change of color at the temperature required to effect a solder termination. While the thermochromic ink ring performed significantly better than the bi-alloy solder ring, it still leaves much to be desired as an effective visual indicator of soldering reliability.
The basic problem with present soldering sleeves is derived from the fact that the heat is, of necessity, externally applied. In an ideal soldering application using MIL-STANDARD 2000 ground rules, the heat would be applied to the inner wire or braid and the solder would be drawn to the heat. In this scenario, the thermochromic ink ring could function as a good indicator of proper heat content at the solder joint, as the lower metal layer would be at the proper eutectic temperature. However, all soldering sleeves must be larger than the wire package to facilitate assembly. This clearance negatively affects the amount of heat effectively transferred from the external source to the inner metal layer. Therefore, the thermochromic ink ring will often indicate a higher temperature than the lower metal layer. Thus, one runs the risk of reading a "false positive", and thereby misjudging the actual quality of the solder joint wetting.
Therefore, a need existed to provide an improved soldering sleeve. The improved soldering sleeve must improve the heat transfer characteristics of previous soldering sleeves. The improved soldering sleeve must be able to absorb heat at a faster rate than previous soldering sleeves thereby reducing the total amount of time that an external heat source needs to be applied for the solder joint to reach an eutectic temperature. The improved soldering sleeve must provide a visual cue to show that proper wetting has been obtained and that the external heat source may be removed.